Synchronizing system and method



June 30, 1942. N, F SMITH, JR 2,288,554A

sYNcHRoNIzNG sYsmEM'AND METHOD Filed May 24; 1940 pulses.

Patented June 30, 1942 sYNcnnomzmG SYSTEM AND iun'rnonV Newland F.Smith, Jr., Wyndmoor, Pa., assignor to. Philco Radio and TelevisionCorporation, Philadelphia, Pa., a corporation of Delaware ApplicationMay 24, 1940, Serial No. 337,059

' l In Great Britain June 5,1939.

s claims. (c1. 17a-69.5)

This invention relates to synchronizing circuits and in lparticulartosynchronizing circuits as used in connection with television receiversand the like. The invention has for its generalobject toprovide a -gasdischarge tube oscillator adapted to synchronize in response to pulsesinvented from exercising any control over the electron current in thetube. Accordingly, by the present invention, there is n provided in asynchronizable oscillator which eluded as a part of the compositetelevisionsignal, and which is not appreciably. aiected inits operationbythe 'presence of undesired noise Furthermore, the oscillator exhibitsno appreciable tendency to fire orto be synchronized on pulsescontainedinthe signal other than those on which it is intended to be sosynchronized;for example, there is no tendency for the, oscillator tobeaffected by the double frequency or "equalizing pulses sometimesincludedin the television signal.

employs a grid-controlled gas discharge tube to control the iiow Voi.'current from an electrical circuitvfor 'generating a sawtooth orlikewave form, means for quenching or blocking the input circuit of the gastube whereby it is made entirely non-responsive to signals ci reasonableamplitude during its active period as well as during its passive period,said means comprising an impedance inserted in the cathode circuit ofthe vgas tube across which there is built -up a voltage which iseffective to bias the tube oit at least throughout the active period.

In copending application of Frank J. Bingley,

Serial No'. 224,646. filed Aug.12,"1938, it is pointed out thatoscillators of the classl which includes the blocking oscillator-andthelike are characterized in that their cycles oifoperation may be periods.During the so-called inchoation period,

the .oscillator issubject to being fired by an incoming synchronizingpulse;` During the active period, the tube which constitutes the heartof the oscillator is conducting` and signals applied tothe input areeiiective to iniiuence the magni- The invention will be understood byreference to the drawing, the two gures of which show certainembodiments of the invention.

In Fig. 1 there is shown an oscillatory device 4for generating a voltageoi 'substantially'.saw-

'- tooth wave form timed by means of substantially divided into threeperiods, which 4may be referred i to as the active, the passive and theinchoationl tude and energyfcontent of the signal produced Y in theoutput circuitv of the oscillator. During the passive period', the tubeis cut off and is incapable of being' fired by any signal of reasonablemagnitude applied 'to its input. aforementioned application, there aredisclosed cer'tain methods of and means for preventing the i signaldeveloped in the output' circuits of such oscillators from beinginiiu'enced by noise and other signals applied to the input circuitsduring In the periodically recurrent pulse signals. AThe-circuitcomprises a condenser 3 which is charged by a battery I4 through aresistor 5. Effectively in shunt with the condenser there is provided agrid controlled gas discharge device 2 to the grid .of which may besupplied from the source shown,

the synchronizing pulses l I for controlling the operation of theoscillator. In the 'absence of synchronizing pulses, the oscillator justdescribed 4' will oscillate at a frequency determined by characteristicsVof th'e gas discharge devicel. The

, condenser will be charged to a point at which the the active period.This is accomplished, ini general, by feeding back a suitable signalfrom the output of the oscillator to block its input during the activeperiod.

Further, inthe said appncation it is observed that the principles mightbe extended and ap plied to synchronizable oscillators employinggrid-controlled gasdischarge tubes. In Fig.. 13, of the said applicationfor example, a circuit is shown in which a signal is derived from theoutput of a gas tube oscillator and applied to block voltage on theplate oi.' the gas discharge device is vsuch as to cause it to conduct,at which time` the condenser will be discharged through its dischargepath. 'I'he potential at which the device conducts will be dependentupon the voltage applied between. its grid and cathode. Thus when asynchronizing pulse of positive polarity l isapplied to the grid of thetube the plate voltage necessary to cause the tube to conduct will b'ereduced to an extent dependent upon the magnitude of the pulse signal.VAssuming that the condenser has been charged for an appreciable time, apulse signal may be applied to the grid the input of Vor to -quenchthe'tube during its conductive period, so that although ionic conductioncontinues to take place the grid is preof the tube which will cause thetube immediately to conduct and to` discharge the condenser. There isalso provided inthe cathode circuit of the gas discharge device inaccordance with the,

invention an impedance comprising a' resistor shunted by a condenser,for developing a voltage whichl is such as appreciably to reduce thecontrolling eiect of the grid upon the operation of the device during apart oi' the interval between the successive synchronizing pulses whichit is desired should actuate the gas discharge device. If the condenser9 is very small, for example not appreciably greater than thedistributed capacity of the resistor 8, the voltagef developed acrossthe'impedance combination will be a pulse signal substantiallycorresponding in duration to the current pulse in the gas dischargedevice occurring during .the discharge of the condenser 3. Such avoltage pulse is adapted to reduce the controlling eifect of the gridupon the current in the gas discharge device during this dischargeperiod which is desirable since it will help to insure the peaks of thesawtooth voltage being of substantially constant amplitude. It mayhowever be desirable to provide protection during a greater portion ofthe time interval between successive synchronizing pulses. With this inmind the condenser may be made larger whereby the voltage developedacross the combination will be of substantially sawtooth form asindicated by the broken line at I0. Such a quenching voltage is adaptedto reducel the susceptibility of the gas dischargedevice toactuation byextraneous pulse signals occurring beztween the desired synchronizingpulses. Invparticular it may operate to exclude the undesirable valternate double horizontal frequency pulses occurring before and afterthe vertical synchronizing pulse in the usual form of televisionsynchronizing signal. In general the time constant of the combinationcomprising the resistor 8 and the condenser 9 should be of substantiallythe same order ofmagnitude as the time interval between successsiv'esynchronizingpulses. However it is to be understood that there may beconsiderable variation from this.

Other impedance combinations may be employed for the purpose ofbroadening the impulse of quenching voltage developed in the cathode andcircuit. For example in Fig. 2 a

`the cathode circuit of the gas discharge device the desired quenchingvoltage. Other impedance combinations will occur to those skilled in theart suitable for obtaining the results desired in accordance with theprinciples herein set forth. f

I claim:

l. In a television system, apparatusl for gen--4 erating deflectingwaveforms, comprising a condenser across which said deflecting waveformis developed, means including a s ource of voltage for charging saidcondenser, means including a grid-controlled gas-discharge device havingat least an anode, a cathode-and a control grid for resonant circuitcomprising the inductance I3 A and the condenser Il is utilized for thispurpose. 1 fIt will be noted that the rest of the circuit issubstantially the same as thatshown in Fig. 1. When the gas, dischargetube 2 is rendered conductive by means'of a synchronizing pulse `appliedto its grid, the condenser i4 is suddenly charged tov a positivepotential with respect to ground. Then, when the tube 2` ceases toconduct due to reduction in its plate voltage brought` the frequency ofoccurrence ofthe synchronizing pulses which it is desired should actuatethe gas discharge device the quenching voltage may be of the form shownat Il. Although this voltage will have decreased sufficiently by thetime the next synchronizing pulse arrives to permit the gas dischargedevice to be actuated thereby, it is nevertheless' suflicently positivein the middle of the interval between successive pulses to exdischargingsaid condenser in response to pulse signals appled to the grid-cathodecircuit of saidy device, a source of desired and undesired pulse signalscoupled to said 'grid-cathode circuit, saidl desired pulse signals beingsubstantially periodii cally recurrent, and impedance means connected' f1n the Agrid-cathode circuit of saidgas-discharge device and responsiveto a pulse v,offcurr'entprod uced therethrough in response to 'oneof-said desired pulse signals for developing in said griding desiredpulse signal but which is substantially dissipated prior .to theoccurrence of sa'idffj next pulse signal, said voltage being ofrsuicientmagnitude during said portion of the intervalt'o f substantially preventthe actuation ofsaid gasdischarge device by said undesired pulsesignals.

2. In a television system, v'apparatus vfor'generating deflectingwaveforms, comprising ra condenser across which said Adeflectingwaveform is developed, means including a source of voltage for chargingsaid condenser, means including a grid-controlled gas-discharge devicehaving at L least an anode, a cathode and a control grid for dischargingsaid condenser invresponse to pulse clude the undesired double frequencyhorizontal v pulse occurring between the desired synchronizing pulsesand represented in the ligure by the signals applied to thegrid-*cathode circuit of said device, a source of desired and undesiredpulse signals coupledto said-grid-cathode circuit, said desired pulsesignals being substantially periodically recurrent, and means comprisinga resistor sired pulse signal but which issubstantially dissipated priorto the occurrenc'of .said next pulse signal, said voltage being ofsulcient magnitude during said portion of theinterval to substantiallyprevent the actuation of said gas-discharge device by said undesiredpulse signals.

3.v In a television system, apparatus for generating deflectingwaveforms, comprising a condenser across which saidjdectingwaveform is-for charging said condensenmeans including a grid-controlledgas-discharge device having at least an anode, a cathode and a controlgrid for discharging said condenser in response to pulse signals.applied to the grid-cathode circuit of said device, a source of desiredand undesiredA i 2,288,554 developed, means including a source ofvoltagev l constant of the order of magnitude of the interi vals betweensuccessive desired pulse signals and being adapted to respond to a pulseof current produced through said device in response to one of saiddesired pulse signals, for developing in said gri'd-cathode circuity avoltage which persists throughout a substantial portion of the intervalbetween said desired pulse signal and thev next -succeeding desiredpulse signal but which is substantially dissipated 'prior to theoccurrence of said next pulse signal, said voltage being v`of sufficientmagnitude during said portion of y the interval to substantially preventthe actuation ofsaid gas-discharge device by said undesired pulsesignals.

4. In a television system, apparatus for generating deflectingwaveforms, comprising a -condenser across which "said deflectingwaveform is developed, means including a source of voltage for chargingsaid condenser, means including a grid-controlled gas-discharge devicehaving at least an anode, a cathode and a control Vgrid for' dischargingsaid condenser in response to pulse signals applied to the grid-cathodecircuit of said device, a source of desired and undesired pulse.V

signals coupled to said grid-cathode circuit, said desired pulse signalsbeing substantially periodically recurrentand means comprising aparallel resonant circuit included in the grid-cathode circuit of saidgas-discharge'device and responsive to a pulse of current produced'therethrough in f response to one of said desired pulse signals fordeveloping in saidgrid-cathode circuit a voltage which persiststhroughout a substantial portion 'of thelinterval between said desiredpulse signal and the next succeeding'desired pulse signal but which` issubstantially dissipated prior to the occurrenceof said next pulsesignal, said voltage being of sufficient magnitude during said portion avoltage which persists throughout a substantial' portion of the intervalbetween said-desired pulsesignal and the next succeeding desired pulsesignal butiwhich is substantially dissipated 'prior to the occurrence ofsaid next pulse signal, said voltage being of suiiioient magnitudeduring said,

portion of the interval to substantially prevent theV actuation of saidgas-discharge device by said unv desiredpulse signals. v

6. In'a vtelevision system, apparatus for generating deflectingwaveforms, comprising a condenser across which said deflecting waveformis developed, means including a source of voltage for charging saidcondenser, means including a grid-controlled gas-discharge device havingat least an anode, a cathode and a control grid for discharging saidcondenser in response to pulse signals applied to thexgrid-cathodecircuit of said device, a source of desired and undesired pulse vsignalscoupled to said grid-cathode circuit, said desired pulse signals beingsubstantially periodically recurrent, and impedance means connected inthe `grid-cathode circuit of said. gasdischarge device and responsive toa pulse of current produced therethrough in response to one of saiddesired` pulse signals 'for developing in` said grid-cathode circuit avoltage impulse of substantially greater duration than the currentimpulse producing it whereby it is effective during a substantialportion of the interval between said desired pulses to prevent theactuation of said gas-discharge device-by undesired pulse signals.

7. In a television system, apparatus for generating deflectingwaveforms, comprising a condenser across which said deflecting waveformis developed, means including a source of voltage for chargingsaidcondenser; means including a gridcontrolled gas-discharge devicehavingat least -an anode, a cathode and a control grid for dischargingsaid condenser in response to pulse signals applied to the grid-cathodecircuit of 'said device, a source of desired and undesired pulse signalscoupled vto said grid-cathode circuit, said desired pulse signals beingsubstantially periodically recurrent and said undesired vpulse sig--nals including pulses. of amplitude comparable tol said desired pulses,occurring in the intervals between said*` desired -pulses andlsubstantially equally spaced with respect to adjacent desired pulses,and impedance means connected in gridcathode circuit of saidgas-discharge device vand responsive to a pulse of cui-rent producedtherethrough fin response to one of said desired pulse signals fordeveloping in said grid-cathode circuit i a voltage which persiststhroughoutv a substantial portion ofthe interval between said desired Ypulse signal and the next succeeding desired pulse discharging saidcondenser in response to pulse signalsapplied to thegrid-cathode circuitof said device, a source of desired and undesired pulse signals coupledto said grid-cathode circuit, said desired pulse signals beingsubstantially periodically recurrent, and aparallel resonant circuitincluded in the grid-cathode lcircuit o f said gas-discharge device,said resonant circuit being tuned to a frequency lower than that atwhichsaid desiredlpulse signalsoccur and being adaptedto respond to apulse of current produced through said device in response to one of saiddesired pulse signals, for developing in said grid-cathode circuitsignal but whichis substantially dissipated prior to the occurrence ofsaid next pulse signal, said voltage being of .s ufiicient magnitudeduring said vportion of the interval to substantially prevent thelactuation of said gas-'discharge device by said undesired pulsesignals.

8. In a television system, apparatus for generating deflectingwaveforms, comprising a condenser across which said deflecting waveformis developed, means for alternately charging and discharging saidcondenser, said means including,

v a grid-controlled space discharge device having at least an anode, acathode and a control grid andbeing adapted for actuation by pulsesignals,

' a source of desired and undesired pulse signals coupled to thegrid-cathode circuit of said device, said desired pulse signals beingsubstantially periodically recurrent, and impedance means connected inthe grid-cathode circuit of said space discharge device and responsiveto a pulse of current produced therethrough in response to one of saiddesired pulse signals for developing in said grid-cathode circuit avoltage which persists 5 throughout a substantial portion o! theinterval between said desired pulse signal and the next succeedingdesired pulse signal but which is suinstantially dissipated prior to theoccurrence of said next pulse signal. said voltage being of sufcientmagnitude during said portion of the interval to substantially preventthe actuation of said space discharge device by said undesired pulsesignals.

/ t NEWLAND F. SMITH, Jn.

